Method of coloring aluminum oxide layers

ABSTRACT

1:2 chromium complex dyes of the formula                    
     in which 
     R signifies C 1-9 -alkyl or a radical of the formula                    
     R 1  signifies C 1-4 -alkyl, —COOM, —COOR 5  or —CONH 2 , 
     R 2  signifies hydrogen or —SO 3 M, 
     R 3  signifies hydrogen, methyl or methoxy, 
     R 4  signifies hydrogen, methyl, methoxy or chloro, 
     n signifies from 0 to 3, 
     M signifies hydrogen or a non-chromophoric cation and 
     Kat +  signifies hydrogen or a non-chromophoric cation 
     are suitable for dyeing artificially produced oxide layers on aluminium or aluminium alloys and so give highly lightfast dyeings in orange shades.

Structures, articles or parts made of aluminium or aluminium alloys and provided with a protective oxide layer, in particular an oxide layer produced electro-chemically by anodization, are nowadays increasingly used in engineering and construction as, for example, a component and/or for the decoration of buildings or means of transport or for utility or artistic articles. For the aesthetic design of such structures, articles or parts they or their oxide layers are frequently dyed. It is therefore desirable for the dyed layers to retain their coloured design for as long as possible and, consequently, for them to have very high levels of fastness to environmental influences, especially to the action of sunlight.

GB-A 703949 discloses copper and cobalt complexes of moroazo dyes of the 2-aminophenol-4,6-disulphonic acid→1-phenyl-3-methyl-5-pyrazolone type, which are used, inter alia, to dye anodic oxide layers on aluminium.

CH-A 396256 discloses heavy-metal complexes of monoazo dyes containing phosphonic acid groups which are used, inter alia, to dye anodic oxide layers on aluminium. Example 10 of CH-A 396256 describes a yellow chromium complex of the monoazo dye made from 2-aminophenol-4,6-disulphonic acid→3-acetoacetylaminobenzenephosphonic acid.

It has now been found that the 1:2 chromium complex dyes defined below are outstandingly suitable as orange dyes for such oxide layers, especially for anodized aluminium or anodized aluminium alloys, and are notable for their surprisingly high light fastness.

The invention relates to the dyeing of oxide layers produced artificially (principally galvanically) on aluminium or aluminium alloys with the 1:2 chromium complex dyes defined below, and to preparations of these 1:2 chromium complex dyes that are particularly suitable for this purpose.

The invention therefore firstly provides a method of dyeing oxide layers produced artificially on aluminium or aluminium alloys, which is characterized in that the dye employed comprises at least one 1:2 chromium complex dye of the formula

in which

R signifies C₁₋₉-alkyl or a radical of the formula

R₁ signifies C₁₋₄-alkyl, —COOM, —COOR₅ or —CONH₂,

R₂ signifies hydrogen or —SO₃M,

R₃ signifies hydrogen, methyl or methoxy,

R₄ signifies hydrogen, methyl, methoxy or chloro,

n signifies from 0 to 3,

M signifies hydrogen or a non-chromophoric cation and

Kat⁺ signifies hydrogen or a non-chromophoric cation.

The alkyl radicals occurring in the formula (I) may be linear or, if they contain three or more carbon atoms, may also be branched, or, if they contain six or more carbon atoms, can also be cyclic.

In the definition of R₁ and R₅ the lower-molecular alkyl radicals are preferred, in particular ethyl and above all methyl.

Among the alkyl radicals in the definition of R the branched and the cyclic are preferred, especially C₄₋₈-isoalkyl, secondary C₃₋₈-alkyl, unsubstituted cyclohexyl and cyclohexyl which carries from one to three methyl groups as substituents. According to one embodiment of the invention preferred alkyl radicals in the definition of R are those which contain at least 4 carbon atoms.

In the radicals of the formula (a) the respective substituents can be located in any desired positions on the phenyl radical; if R₂ is a sulpho group —SO₃M, this group is preferably located in meta position or para position; if R₃ is methyl or methoxy, and/or if R₄ is methyl, methoxy or chloro, these substituents can be located in any of the available positions, with preferably at least one of the two ortho positions of the phenyl radical being unsubstituted. With particular preference both R₃ and R₄ are hydrogen.

The free bond on the naphthalene radical of the formula (b) can be located arbitrarily in α or β position, the α position being preferred. For n=1 to 3 the n sulpho groups in the formula (b) can be located in n arbitrary available positions, the vicinal positions to the bond to the pyrazole ring preferably being unsubstituted. Mention may be made in particular of α-naphthyl, β-naphthyl and the following naphthylsulphonic acid radicals of the formula (b): 2-naphthyl-4,6,8-trisulphonic acid, 1-naphthyl-3,6-disulphonic acid, 1-naphthyl-3,7-disulphonic acid, 1-naphthyl-4,6-disulphonic acid, 1-naphthyl-4,7-disulphonic acid, 2-naphthyl-4,8-disulphonic acid, 2-naphthyl-5,7-disulphonic acid, 2-naphthyl-6,8-disulphonic acid, 1-naphthyl-3-, -4-, -5-, -6- or -7-sulphonic acid and 2-naphthyl-5- or -6-sulphonic acid. Among these radicals, preference is given to those in which n=1, especially 1-naphthyl-4- or -5-sulphonic acid.

Particular preference in the definition of R is given to sulphophenyl or, in particular, unsubstituted phenyl.

The carboxylic and sulphonic acid groups can be in the form of the free acid or, preferably, in the form of salts of non-chromophoric cations.

M and Kat⁺ can each be hydrogen or a non-chromophoric cation. Hydrogen as ion is present as the hydronium ion. Examples of suitable non-chromophoric cations are alkali metal cations, ammonium cations and alkaline earth metal cations. As alkaline earth metal cations mention may be made, for example, of calcium and magnesium. As ammonium cations mention may be made of unsubstituted ammonium or also ammonium ions of low-molecular amines, e.g., mono-, di- or tri-C₁₋₂-alkyl- and/or -β-hydroxy-C₂₋₃-alkyl-ammonium, examples being mono-, di- or tri-isopropanolammonium, mono-, di- or triethanolammonium, N-methyl-N-ethanol-ammonium. Suitable alkali metal cations are customary such cations, examples being lithium, sodium and/or potassium ions. Among these cations the alkali metal cations and ammonium cations are preferred. In one embodiment of the invention some of the symbols M and Kat⁺ are hydrogen and the rest of them are alkali metal cations and/or ammonium cations.

The 1:2 chromium complex dyes of the formula (I) can be symmetrical or also asymmetrical complexes; i.e., apart from the definitions of M and Kat⁺, the two radicals R can have the same definition as or different definitions to one another, and/or the two radicals R₁ can have the same definition as or different definitions to one another. Preference is given to symmetrical chromium complexes of the formula (I); i.e., to those in which the two radicals R have the same definition and in which the two radicals R₁ also have the same definition.

The 1:2 chromium complex of the formula (I), in which R₁ is methyl and R is unsubstituted phenyl, is disclosed in “Chemical Abstracts” as the tetra- and pentasodium salt under the Registry Numbers 68541-69-5 and 68239-48-5.

The 1:2 chromium complex dyes of the formula (I) can be prepared in analogy to chromation reactions which are known per se. In particular, the process for preparing the 1:2 chromium complex dyes of the formula (I) is characterized in that at least one metallizable compound which corresponds in one of its tautomeric forms to the formula

is reacted with a chromium donor compound.

The compounds of the formula (II) can be prepared by coupling the diazo compound of 2-amino-1-hydroxybenzene-4,6-disulphonic acid to a coupling component which corresponds in one of its tautomeric forms to the formula

The compounds of the formula (III) are known or can be prepared in analogy to known methods by acylating an optionally acetylated hydrazine of the formula R—NH—NH₂ with corresponding 1,3-dicarbonyl compounds, especially with corresponding acylacetic esters of low-molecular alcohols (e.g., methyl or ethyl esters) or with acylacetamide, and carrying out ring closure to give the corresponding pyrazolinone, for example, in aqueous, aqueous/organic or organic solution, at mild temperatures, for example, in the range from 0 to 70° C., in particular from 20 to 60° C., for the acylation, and at higher temperatures, for example, from 50° C. to reflux, for the ring closure.

The diazotization of 2-amino-1-hydroxybenzene-4,6-disulphonic acid can be carried out in a manner known per se, in particular with sodium nitrite in an acidic medium (e.g., a pH of 1 to 3) and at a low temperature, for example, in the range from −5 to +15° C. The coupling of the diazonium compound to a coupling component of the formula (III) can be carried out in a manner known per se, advantageously at temperatures in the range from −5 to +30° C., preferably below 25° C, and with particular preference in the range from 0 to 10° C., and under distinctly alkaline conditions, advantageously in the pH range from 8 to 12, preferably from 9 to 11. The reactions may be carried out in an aqueous medium or also in an aqueous/organic medium, the organic medium preferably being a water-miscible inert solvent (e.g., an alcohol or dioxane).

For the chromation of the compounds of the formula (II) to give corresponding 1:2 chromium complex dyes of the formula (I) it is possible to use suitable chromium compounds which are customary per se and as are employed for the preparation of chromium complexes, examples being chromium hydroxide or water-soluble salts of low-molecular carboxylic acids or mineral acids, in particular chromium trichloride, chromium trifluoride, chromic sulphate, chromic formate, chromic acetate, potassium chromium sulphate, ammonium chromium sulphate (e.g., chrome alums) and, if desired, with an addition of a reducing agent, e.g., glucose, also sodium or potassium chromate or dichromate.

Chromation can be carried out directly to the 1:2 chromium complex stage or in stages via the 1:1 chromium complex stage with subsequent complexation to the 1:2 chromium complex stage.

Chromation can be conducted in an aqueous medium, preferably at pH values in the range from 2 to 10 and at temperatures in the range from 95 to 130° C., under pressure if necessary. If desired, the reaction may be carried out with addition of organic solvents or also only in organic solvents. Suitable organic solvents are preferably those which are miscible with water and have a boiling point of more than 100° C. and in which the azo dyes and their metal salts are soluble, examples being glycols, ether alcohols or amides (e.g., ethylene glycol, polyethylene glycols, β-ethoxyethanol, β-methoxy-ethanol, formamide or dimethylformamide). To prepare asymmetrical 1:2 chromium complex compounds chroming can be carried out in stages by first preparing the 1:1 chromium complex of one of the complexing compounds and then preparing the 1:2 chromium complex from the first complex using a second complexing agent. The 1:1 chromium complexes can be prepared in a manner known per se, e.g. under conditions analogous to those for the 1:2 chromium complexes, but, preferably, at more strongly acidic pH values, advantageously at a pH<3. The preparation of the 1:2 chromium complexes then takes place preferably at pH values in the range from 3 to 10, preferably from 4 to 9.

After having carried out the required coupling and metallization and, if required, salt formation or ion exchange in order to introduce cations M and/or Kat⁺, the resulting dyes or dye mixtures may be isolated from the mother liquor in a manner known per se; for example, by precipitation or recrystallization by addition of salt, primarily NaCl or KCl, (=salting out) or a strong mineral acid, for example, hydrochloric acid, sulphuric acid or phosphoric acid (=acidification), and filtration, or, for example, by membrane filtration of the dye solution (either of the dye solution as prepared or of the solution of the filtered dye) and, if desired, drying (e.g., by spray drying) of the dye solution, that has optionally been desalinated by membrane filtration. If desired, the dye may be blended with a customary conventional extender, for example, with non-electrolytic extenders; the dye desalinated by membrane filtration may be blended, if desired, with non-electrolytic extenders (principally urea and/or oligosaccharides, e.g., dextrins), before or after drying (e.g. spray drying). If desired, anionic surfactants, especially hydrocarbonsulphonates or other organic sulphonates, e.g., sulphonated castor oil, sulphosuccinates or ligninsulphonates and/or dedusting agents can be added to the dyes, particularly for dry formulations. If a surfactant or dedusting agent is used the weight ratio thereof to the pure dye is advantageously at values in the range from 1:99 to 5:95. For liquid formulations the dyes, advantageously in desalinated form and without extender additives, are produced as concentrated solutions in which the dye content lies advantageously in the range from 5 to 35 percent by weight, preferably from 10 to 25 percent by weight, based on the weight of the composition. optionally, it is also possible to add an additive for combating the damaging effect of microorganisms (for example, an agent which kills the microorganisms, i.e., a microbicide, or which inhibits their growth, i.e., primarily a bacterial, fungal and/or yeast growth-inhibiting additive) in concentrations, for example, of from 0.001 to 1% by weight based on the overall liquid formulation.

The dyes of the formula (I), especially in the form of their salts, in particular alkali metal salts and/or ammonium salts, are highly soluble in water and, in dry form or alternatively in the form of even their concentrated solutions, are very stable on storage and transportation. They serve as anionic dyes, for dyeing artificially produced oxide layers on aluminium or aluminium alloys.

Aluminium alloys which come mainly into consideration are those in which the aluminium component is predominant, especially alloys with magnesium, silicon, zinc and/or copper, e.g., Al/Mg, Al/Si, Al/Mg/Si, Al/Zn/Mg, Al/Cu/Mg and Al/Zn/Mg/Cu, preferably those in which the aluminium content accounts for at least 90 percent by weight; the magnesium content is preferably ≦6 percent by weight; the silicon content is preferably ≦6 percent by weight; the zinc content is preferably ≦10 percent by weight; the copper content is advantageously ≦2 percent by weight, preferably ≦0.2 percent by weight.

The oxide layers formed on the metallic aluminium or on the aluminium alloys may have been generated by chemical oxidation or, preferably, galvanically by anodic oxidation. The anodic oxidation of the aluminium or of the aluminium alloy for passivation and formation of a porous layer can take place in accordance with known methods, using direct and/or alternating current, and using electrolyte baths that are suitable in each case, with the addition, for example, of sulphuric acid, oxalic acid, chromic acid, citric acid or combinations of oxalic acid and chromic acid or sulphuric acid and oxalic acid. Such anodizing Techniques are known in the art, examples being the DS process (direct current; sulphuric acid), the DSX process (direct current; sulphuric acid with addition of oxalic acid), the DX process (direct current; oxalic acid), the DX process with addition of chromic acid, the AX process (alternating current; oxalic acid), the AX-DX process (oxalic acid; first alternating current then direct current), the AS process (alternating current; sulphuric acid) and the chromic acid process (direct current; chromic acid). The voltages lie, for example, in the range from 5 to 80 volts, preferably from 8 to 50 volts; the temperatures lie, for example, in the range from 5 to 50° C.; the current density at the anode lies, for example, in the range from 0.3 to 5 A/dm², preferably from 0.5 to 4 A/dm², current densities of just ≦2 A/dm² generally being suitable for producing a porous oxide layer; at higher voltages and current densities, for example, in the range from 100 to 150 volts and ≧2 A/dm², especially from 2 to 3 A/dm², and at temperatures up to 80° C., it is possible to produce particularly hard and fine-pored oxide layers in accordance, for example, with the “Ematal” process with oxalic acid in the presence of titanium salts and zirconium salts. For the production of oxide layers which subsequently are dyed electrolytically or are directly dyed adsorptively with a dye of the formula (I) the voltage, in accordance with a preferred procedure which is customary per se in practice, lies in the range from 12 to 20 volts; the current density in this case is preferably from 1 to 2 A/dm². These anodizing techniques are common knowledge in the art and are also described in detail in the technical literature: for example, in Ullmann's “Enzyklopädie der Technischen Chemie”, 4th edition, volume 12, pages 196 to 198, or in the Sandoz brochures “Sanodal®” (Sandoz AG, Basle, Switzerland, publication No. 9083.00.89) or “Ratgeber für das Adsorptive Färben von Anodisiertem Aluminium” (Sandoz, publication No. 9122.00.80). The thickness of the porous oxide layer lies advantageously in the range from 2 to 35 μm, preferably from 2 to 25 μm. In the case of colour anodization the thickness of the oxide layer amounts advantageously to values in the range from 5 to 60 μm, preferably from 10 to 40 μm. The dyes of the formula (I) are also suitable for thin oxide layers, e.g., those ≦10 μm, and for those which have been anodically dyed. If the anodized aluminium or the anodized aluminium alloy has been stored for a short time (e.g., 1 week or less) prior to dyeing it is advantageous to wet and/or activate the substrate prior to colouring by means, for example, of treatment with a non-reductive aqueous mineral acid, for example, with sulphuric acid or nitric acid. If desired, the oxide layer—in analogy to the known “Sandalor®” process—can first be electrolytically predyed, for example, in a bronze shade, and then overdyed with a dye of the formula (I); in this way it is possible to obtain particularly muted shades which find a particularly suitable use, for example, in exterior architecture. It is also possible to overdye oxide layers predyed by colour anodization (by the process known as integral dyeing) with a dye of the formula (I); in this way too it is possible to obtain muted shades which are particularly suitable, for example, for exterior architecture.

To dye the oxide layer with the dyes of the formula (I) it is possible to use dyeing methods which are customary per se, in particular adsorption methods, where the dye solution can be applied, for example, to the oxide surface by means, for example, of spraying or by application with a roller (depending on the shape of the substrate) or, preferably, by immersion of the article to be dyed in a dyebath. In one feature of the dyeing method of the invention the anodized metal articles can, following anodic treatment and rinsing, be treated with the dyebath in the same vessel in which anodizing has taken place, or, in a further feature, the articles to be dyed may, following anodic treatment and rinsing, be removed from the vessel and be dyed, either directly or after drying and any intermediate storage, in a second unit; if the articles have been stored in the interim, it is recommended to carry out activation (for example, by brief treatment with sulphuric or nitric acid) prior to dyeing. Regarding this point it is noted that intermediate storage—if carried out at all—is preferably for a limited, short period, for example, less than 1 week, especially ≦2 days. In accordance with generally customary and preferred processes, dyeing takes place directly after anodizing and subsequent rinsing.

Dyeing takes place judiciously at temperatures below the boiling point of the liquor, advantageously at temperatures in the range from 15 to 80° C., preferably in the range from 20 to 75° C. and, with particular preference, from 20 to 60° C. The pH of the dyeing liquor lies, for example, in the clearly acidic to weakly basic range, for example, in the pH range from 3 to 8, with preference being given to conditions ranging from weakly acidic to nearly neutral, in particular in the pH range from 4 to 6. The dye concentration and the duration of dyeing may vary very greatly depending on the substrate and on the desired colouring effect. Suitable dye concentrations are for example those in the range from 0.01 to 20 g/l, advantageously from 0.1 to 10 g/l and, in particular, from 0.2 to 2 g/l. The dyeing duration may lie, for example, in the range from 20 seconds to 1 hour, advantageously from 5 to 40 minutes, with very fine, intense dyeings being obtainable at a dyeing duration of only from 5 to 30 minutes on oxide layers having a thickness in the range from 5 to 25 μm at dye concentrations, pH values and temperatures within the preferred ranges. Since the dyes to be employed in accordance with the invention are highly soluble in water it is also possible to use them to prepare stock solutions or reinforcing liquors of any desired concentration in order to set or correct the dye concentration in the dyebath to whatever level, as required.

Prior to sealing, the dyed substrate is advantageously rinsed with water. Sealing can be carried out using any known methods customary per se, with or without the aid of suitable additives. Sealing may be carried out, for example, in one or two stages, and, if proceeding in two stages, the first stage consists advantageously of treatment with hot water (for example, in the temperature range from 70 to 90° C.). For the second stage (aftersealing or main sealing) or for the single-stage process sealing may be carried out for example by boiling, with deionized water (for example, at temperatures ≧95° C., at pH values in the range from 5.5 to 6, and for a treatment duration of from 30 to 60 minutes) or a steam treatment can be carried out, for example, at from 4 to 6 bar overpressure. In accordance with a further procedure sealing may be carried out, for example, at pH values in the range from 4.5 to 8, with the aid of metal salts or metal oxides (e.g., nickel acetate or cobalt acetate) or also with chromates, in one stage or two stages. Such sealing with metal compounds (e.g., with nickel acetate) permits particularly effective suppression of dye bleeding. A further procedure operates with the aid of organic sealants, e.g. organic phosphonates and diphosphonates or also water-soluble (cyclo)aliphatic polycarboxylic acids or aromatic ortho-hydroxycarboxylic acids (as described, for example, in DE-A-3327191) at pH values in the range, for example, from 4.5 to 8. The sealants can be employed in very low concentrations: for example, in concentrations from 0.001 to 2 g/l, preferably from 0.002 to 0.1 g/l. The sealing temperature can vary depending on the auxiliary used and on the process chosen; for example, in the range from 20 to 100° C., for hot sealing e.g. in the range from 60 to 100° C., advantageously from 80 to 100° C., for cold sealing e.g. at temperatures in the range from 20 to 30° C., with the possible use of nickel salts or cobalt salts in combination with alkali metal fluorides, e.g., NaF, in particular also for cold sealing, at, for example, 20-30° C. If desired, the dyed and sealed aluminium oxide layers or aluminium alloy oxide layers can subsequently be coated with, for example, waxes, resins, oils, paraffins or plastics, provided that this coating is transparent.

For setting the pH values in the dyebaths and sealing solutions it is possible to use known additives which are customary per se, examples being sulphuric acid, acetic acid, ammonia, sodium hydroxide or sodium carbonate, and/or sodium acetate. If desired or necessary, antismut additives can be used and/or surfactants (e.g., wetting agents), especially anionic surfactants such as C₉₋₁₄-alkanesulphonates, mono- or dialkylbenzenesulphonates in which the alkyl radicals contain a total of 4 to 18 carbon atoms, and oligomeric condensation products of formaldehyde and naphthalenesulphonic acids.

The dyeings obtainable with the dyes of the formula (I) feature very fine, bright orange shades and are notable for their high levels of fastnesses, especially light fastness, (also light fastness when wet and weathering fastness), especially with those dyes in which R is a radical of the formula (a) and, in particular, in which the formula (a) denotes unsubstituted phenyl.

In the examples which follow the parts signify parts by weight and the percentages signify percentages by weight; the temperatures are indicated in degrees Celsius.

EXAMPLE 1

13.45 g (0.05 mol) of 2-amino-1-hydroxybenzene-4,6-di-sulphonic acid are placed in 40 ml of water and a pH in the acidic range is set with 3 ml of hydrochloric acid. With ice cooling, 3.5 g (0.0507 mol) of sodium nitrite dissolved in 5 ml of water are added and the mixture is subsequently stirred at between 0° C. and 10° C. for 2 hours. The excess nitrite is destroyed with a little sulphamic acid. The pH is adjusted to 5 to 6 with dilute sodium carbonate solution. This diazonium salt solution is added dropwise at between 0° and 10° C. to a solution of 8.7 g (0.05 mol) of 3-methyl-1-phenyl-5-pyrazolone in 20 ml of water to which 30 g of ice are added, this solution having been rendered alkaline, heated to 50° C. and then cooled to from 0° to 10° C. beforehand. Stirring is continued for 4 hours. To this reaction solution there are added 5 ml of formic acid and 0.025 mol of chromium sulphate. The pH is adjusted to 5 to 6.5 with 30% sodium hydroxide solution and the mixture is boiled for 6 hours. The product is precipitated with potassium chloride and filtered. The chromium complex dye of the above structure is obtained, in a yield of 90%, in the form of the sodium/potassium salt.

If desired, the dye prepared can be desalinated by membrane filtration to give, for example, a 15% strength dye solution which is free from other electrolytes.

The maximum light absorption λ_(max) of the dye, measured as a solution with a concentration of 26.57 mg/l in 1% strength sodium carbonate solution, is at 495.4 nm. The specific extinction is 22580 cm²/g (=22.58 l/g·cm).

The dyes listed in the following table which, in the form of the free acid, correspond to the following formula (2)

in which the symbols R′ and R′₁ are as defined in Table 1, are produced in analogy to the procedure described in Example 1 and are obtained in analogy to Example 1 in the form of their sodium/potassium salts, and give orange dyeings on anodized aluminium.

TABLE 1 (Examples 2 to 20) Exam- ple R′ R′₁  2

—CH₃  3

—CH₃  4

—CH₃  5

—CH₃  6

—CH₃  7

—CH₃  8

—CH₃  9

—CH₃ 10

—CH₃ 11

—CH₃ 12

—CH₃ 13

—CH₂CH₃ 14

—COOH 15

—CONH₂ 16

—COOC₂H₅ 17

—CH₂CH₂CH₃ 18

—CONH₂ 19

—CH₃ 20

—CH₃

Through the use of corresponding bases for neutralization and of corresponding salts for precipitation it is also possible to obtain the dyes of Examples 1 to 20 in the form of their ammonium and/or lithium salts. By acidification, for example, with sulphuric acid, filtration, and neutralization of the dye, which precipitated by addition of acid, with triethanolamine, the dyes can be obtained in the corresponding amine salt form.

Dye Composition 1

99.7 parts of the desalinated 15% strength dye solution prepared in accordance with Example 1 are mixed with 0.3 part of microbicide.

Dye Compositions 2 to 20

As described for the dye composition 1, desalinated 15% strength solutions of the dyes of Examples 2-20 are mixed with microbicide.

Dye Composition 21

20 parts of the filtered and dried dye prepared in accordance with Example 1 are ground together with 80 parts of white dextrin. This gives a uniform dye powder which dissolves readily and completely in water.

Dye Compositions 22 to 40

As described for the dye composition 21, the dried filter cakes of the dyes of Examples 2-20 are ground together with white dextrin in a weight ratio of 20/80. In each case, this gives uniform dye powders which dissolve readily and completely in water.

Dye Composition 41

100 parts of the desalinated 15% strength dye solution prepared in accordance with Example 1 are mixed together with 60 parts of white dextrin and the resulting solution is dried in a spray dryer. This gives a uniform dye powder which dissolves readily and completely in water.

Dye Compositions 42 to 60

As described for the dye composition 41, desalinated 15% strength solutions of the dyes of Examples 2-20 are mixed together with white dextrin and are dried by spray drying. In each case, this gives uniform dye powders which dissolve readily and completely in water.

Dye Composition 61

20 parts of the dye, desalinated by membrane filtration and dried, prepared in accordance with Example 1 are ground together with 80 parts of white dextrin. This gives a uniform dye powder which dissolves readily and completely in water.

Dye compositions 62 to 80

As described for the dye composition 61, the dyes of Examples 2-20, desalinated by membrane filtration and dried, are ground together with white dextrin in a weight ratio of 20/80. In each case, this gives uniform dye powders which dissolve readily and completely in water.

Application Example A

A degreased and deoxidized workpiece of pure aluminium sheet is anodically oxidized in an aqueous solution which comprises sulphuric acid and aluminium sulphate in a concentration of from 17 to 22% sulphuric acid and from 0.5 to 1.5% aluminium ions, at a temperature of from 18 to 20° C., at a voltage of from 15 to 17 volts with direct current having a density of 1.5 A/dm², for 50 minutes. An oxide layer about 20 μm thick is formed. After rinsing with water, the aluminium sheet workpiece is dyed for 20 minutes at 60° C. in a dyebath containing in 1000 parts of deionized water 0.5 part of the chromium complex dye produced according to Example 1, at a pH of from 5.5 to 5.7 (set with acetic acid and sodium acetate). The dyed workpiece is rinsed with water and then sealed in deionized water at from 98 to 100° C. for 60 minutes. To prevent the formation of any disruptive deposit during sealing, an antismut agent can be added to the deionized water that is employed for sealing. An orange-dyed workpiece is obtained which is notable for its outstanding light fastness and weather fastness.

Application Example B

The procedure described in Application Example A is repeated with the difference that sealing is carried out with a solution which contains 3 parts of nickel acetate in combination with 0.5 part of oligomeric condensate of naphthalenesulphonic acid and formaldehyde in 1000 parts of water. An orange dyeing of outstanding light fastness and weather fastness is obtained.

Application Example C

The procedure described in Application Example B is repeated with the difference that the dyeing is carried out for 40 minutes at 40° C. instead of 20 minutes at 60° C. An orange dyeing having excellent light and weather fastness is obtained.

Application Example D

A degreased workpiece made of Peraluman 101 (aluminium alloy with 1% Mg and 0.5% Si) sheet is anodically oxidized in an aqueous solution containing sulphuric acid and aluminium sulphate of a concentration of from 18 to 20% sulphuric acid and from 0.5 to 1.5% aluminium ions, at a temperature of from 18 to 20° C., at a voltage of from 15 to 17 volts with direct current of a density of 1.5 A/dm², for 50-60 minutes. An oxide layer about 22-24 μm thick is formed. After brief rinsing, the anodized aluminium is dyed electrolytically in an aqueous solution of the following components

15-20 g/l of tin(II) sulphate

15-20 g/l of sulphuric acid and

25 g/l of a customary commercial tinning bath stabilizer.

The workpiece is left for 2 minutes at 20-25° C. in the solution without exposure to current and then is dyed electrolytically at a voltage of 16 volts. A medium bronze coloration is obtained. After thorough rinsing in running water, the workpiece is dyed at 60° C. for 20 minutes in a dyebath containing in 1000 parts of deionized water 1 part of the chromium complex dye prepared according to Example 1, at a pH of 5.5 (set with acetic acid and sodium acetate). The dyed work-piece is rinsed with water and then sealed at from 98 to 100° C. for 60 minutes in a 0.3% strength aqueous nickel acetate solution whose pH is set to 5.5-6 with acetic acid. A claret-dyed workpiece is obtained which is notable for its outstanding light fastness and weather fastness.

In Application Examples A, B, C and D, the dye of Example 1 can also be employed in the form of the dye preparation 1, 21, 41 or 61.

The light fastness may be determined in accordance with ISO Standards, for example in accordance with ISO Standard No. 2135-1984, by dry exposure of a sample in exposure cycles of 200 hours each of standard light exposure in an Atlas Weather-O-meter 65 WRC, which is fitted with a xenon arc lamp, or in accordance with ISO Standard No. 105 B02 (USA) by dry exposure of a sample in exposure cycles of 100 hours each of standard light exposure in an Atlas Weather-O-meter Ci 35 A, which is fitted with a xenon arc lamp, and comparison of the exposed samples with a rating sample of light fastness rating=6 on the blue scale (corresponding to a rating of about 3 on the grey scale) or directly with the blue scale original of rating 6. If a light fastness value corresponding to the rating 6 on the blue scale is achieved after only 2 exposure cycles, the sample is evaluated as having a light fastness rating=7; if this point is not reached until after 4 cycles, the sample is accorded a fastness rating of 8, and so on, as set out in Table 2 below.

TABLE 2 Light Exposure time fastness Exposure cycle 65 WRC Ci 35 A rating 1 200 hours 100 hours 6 2 400 hours 200 hours 7 4 800 hours 400 hours 8 8 1600 hours  800 hours 9 16 3200 hours  1600 hours  10

After 8 exposure cycles, all of the dyeings obtained with the dye of Example 1 in accordance with Application Examples A, B, C and D are unchanged, while the dyeing obtained in comparison using the 1:2 cobalt complex dye of Example 2 (feeding liquor) of GB-A 703949 analogously to Application Example B has changed significantly after the eighth exposure cycle (corresponding to a light fastness rate of 9). The dyeing obtained in comparison using the 1:1 copper complex dye of Example 1 of GB-A 703949 analogously to Application Example B has changed significantly after the first exposure cycle (corresponding to a light fastness rating of 6). The dyeing obtained in comparison using the dye of Example 10 of CH-A 396256 analogously to Application Example B has faded after only the first exposure cycle (corresponding to a light fastness rating of 1).

Analogously to the dye of Example 1, the dyes from each of Examples 2 to 20, as such or in the form of the respective dye preparations 2 to 20, 22 to 40, 42 to 60 or 62 to 80, are used in Application Examples A, B, C and D. Orange dyeings are produced in accordance with the instruction in Application Examples A, B and C, and claret dyeings are obtained in accordance with the instruction in Application Example D. These dyeings are distinguished by their light and weather fastness properties. 

What is claimed is:
 1. Method of dyeing oxide layers produced artificially on aluminium or aluminium alloys, said method comprising applying a dye to the oxide layers, wherein the dye employed comprises at least one 1:2 chromium complex dye of the formula

in which R signifies C₁₋₉-alkyl or a radical of the formula

R₁ signifies C₁₋₄-alkyl, —COOM, —COOR₅ or —CONH₂, R₂ signifies hydrogen or —SO₃M, R₃ signifies hydrogen, methyl or methoxy, R₄ signifies hydrogen, methyl, methoxy or chloro, n signifies from 0 to 3, M signifies hydrogen or a non-chromophoric cation, and Kat⁺ signifies hydrogen or a non-chromophoric cation
 2. Method according to claim 1, characterized in that in the 1:2 chromium complex dyes of the formula (I) R signifies a radical of the formula (a), R₁ signifies methyl, R₂ signifies hydrogen or —SO₃M, R₃ signifies hydrogen, R₄ signifies hydrogen, M signifies hydrogen or an ammonium or alkali metal cation and Kat⁺ signifies hydrogen or an ammonium or alkali metal cation.
 3. Method according to claim 2, characterized in that the oxide layer is anodically dyed prior to dyeing with dyes of the formula (I).
 4. Method according to claim 1 for dyeing anodized aluminium and/or anodized aluminium alloys.
 5. Method according to claim 1, characterized in that, after dyeing with dyes of the formula (I), the porous dyed oxide layer is sealed.
 6. Dye compositions which either are desalinated aqueous solutions of the dye of the formula (I) according to claim 1 which, if desired, comprise non-electrolytic additives and, if desired, comprise an additive for combating the damaging effect of microorganisms or are dry preparations which comprise one or more of the said additives and/or comprise at least one surfactant and/or dedusting agent.
 7. Method according to claim 1, characterized in that the dye is employed in the form of a dye composition which either is a desalinated aqueous solution of the dye of the formula (I) which, if desired, comprises non-electrolytic additives and, if desired, comprises an additive for combating damaging effects of microorganisms or is a dry preparation which comprises one or more of said additives and/or comprises at least one surfactant and/or dedusting agent.
 8. Oxide layers dyed by the method according to claim
 1. 9. Method according to claim 1, wherein the dye of formula (I) is applied to the oxide layers by an adsorption method.
 10. Method according to claim 9, wherein the dye of formula (I) is applied to the oxide layers by application of a solution of the dye of formula (I).
 11. Method according to claim 10, wherein the solution of the dye of formula (I) is a desalinated aqueous solution of the dye of the formula (I) which, if desired, comprises non-electrolytic additives and, if desired, comprises an additive for combating damaging effects of microorganisms.
 12. Method according to claim 10, wherein the solution of the dye of formula (I) is either a desalinated aqueous solution of the dye of the formula (I) which, if desired, comprises non-electrolytic additives and, if desired, comprises an additive for combating the damaging effect of microorganisms or a dry preparation which comprises one or more of said additives and/or comprises at least one surfactant and/or dedusting agent.
 13. Method according to claim 9, wherein the application of the solution of the dye of formula (I) is with a roller or by spraying, or by immersion in a dye bath of the dye of formula (I).
 14. Method according to claim 13, wherein the solution or bath of the dye of formula (I) is an aqueous stock solution or a reinforcing liquor.
 15. Method according to claim 13, wherein the solution of the dye of formula (I) is either a desalinated aqueous solution of the dye of the formula (I) which, if desired, comprises non electrolytic additives and, if desired, comprises an additive for combating the damaging effect of microorganisms or a dry preparation which comprises one or more of the said additives and/or comprises at least one surfactant and/or dedusting agent. 